The article “Feasibility Study of Ultrasonic Computed Tomography-Guided High-Intensity Focused Ultrasound” by H. Azhari et al., Ultrasound in Medicine and Biology, volume 38, number 4, pages 619 to 625 (2012) discloses a temperature distribution measuring apparatus for measuring a temperature distribution within tissue during a high-intensity focused ultrasound (HIFU) breast treatment procedure. The apparatus comprises an ultrasound imaging device for generating images depicting the speed of sound within the tissue, wherein based on changes in the speed of sound temperature elevations, which occur during the HIFU breast treatment procedure, are determined.
The article “Ultrasound monitoring of temperature and coagulation change during tumor treatment with microwave ablation” by C. Yang et al., Frontiers of Biology in China, volume 4, number 3, pages 254 to 259 (2009) discloses several methods for estimating a temperature distribution within tissue during a microwave ablation therapy procedure by using correlations between ultrasound characteristics of the tissue and the temperature of the tissue.
The article “Three-dimensional spatial and temporal temperature imaging in gel phantoms using backscattered ultrasound” by A. Anand et al., IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 54(1), pages 23 to 31 (2007) discloses an ultrasound thermometry system being adapted to determine the temperature of an object based on ultrasound signals backscattered by the object. In particular, the system is adapted to determine the speed of sound within the object from the backscattered ultrasound signals and to determine the temperature of the object based on the determined speed of sound.
This kind of determining the temperature of the object requires that the relationship between the speed of sound and the temperature of the object is linear, i.e. the temperature range in which the temperature of the object is measurable by the system is delimited by the temperature range in which the relationship between the speed of sound and the temperature is linear. If the object is heated, the temperature of the object can only be measured, as long as the temperature of the object is within this temperature range, thereby limiting the time period during which the temperature of the object can be measured while heating the object.